In the field of hydrocarbon polymer products it is well known that the application of heat can result in a softening of the product. Furthermore, if a cross-linked polymer product is produced and then allowed to cool to ambient temperatures in a particular configuration, the molecules of the polymer will bond in such a manner that the product will have a "memory" of that original configuration and will tend to resist being reconfigured. For example, cables sheathed in cross-linked polyethylene insulation that are stored on spools may retain an unwieldy, kinked shape when removed from the spool. The kinking greatly increases the difficulty of measuring a desired length of cable, or of threading the cable through a straight conduit.
Similar problems are encountered in the installation of linoleum and have been solved by application of a heating means to the roll of linoleum. For example, U.S. Pat. No. 4,942,287 discloses a heater assembly comprising a heater tube and a heater blanket for heating a roll of linoleum prior to unrolling the linoleum for installation.
Additionally, various methods for heating tubular members are known. U.S. Pat. No. 3,840,349 discloses a sublimation chamber coaxial with a heater that may be wound around the outside of the sublimation chamber or pass through its center. In both embodiments the heater and chamber are relatively rotatable, generally by fixing one and rotating the other.
U.S. Pat. No. 2,697,772 discloses a method for fusing a longitudinal seam in an aluminum cable sheathing by passing the cable wrapped in sheathing through a coiled induction heater. Alternating current passed through the coil causes a voltage difference across the seam, inducing current across the seam when the seam edges are brought together and forming a weld. The induction coil is fixed relative to the cable and forms part of a manufacturing process.
U.S. Pat. No. 4,234,624 discloses a method for applying an insulation of cross-linked polyethylene on a cable conductor wherein cross-linked polymer is extruded around the cable and then heated with radiation energy while the cable is subjected to pressure within a vulcanization tube. The radiation is generated using infrared radiation sources outside the tube, with temperatures exceeding 1100.degree. C.
U.S. Pat. No. 4,460,820 discloses an apparatus for heating a heat shrinkable tube. The apparatus provides a plurality of independently operable heating units supported on a base.
U.S. Pat. No. 3,187,279 discloses a heating means for surface wave conductors Which comprises a conducting spiral wound around the surface wave conductor. U.S. Pat. No. 3,187,279 discloses a particular winding designed to avoid affecting surface wave propagation within the surface wave conductor.
Watlow Electric Heaters and Control, St. Louis, Mo. manufactures a flexible heater that comes in blanket or tape form. Watlow recommends use of the flexible heater in heating polyvinyl chloride conduit or tubing to simplify bending it to the desired shape in the field.
None of the prior art discloses the use of an inexpensive, simple, portable heating apparatus for heating variously sized polyethylene insulated cables in the field. The present invention discloses the use of a flexible heat tape designed to be wrapped in a spiral around a cable and designed to heat the cable insulation to a temperature at which it is malleable in a relatively short time.